Is it OK to use Air Vent power fans in an industrial/commercial application with granite material in the facility with lots of debris?

It is not recommended to use power fans in a manner for which they were not designed.

Air Vent's fans are specifically designed for venting attics above living spaces in a residential application. UL designates Air Vent products as being for residential use only. Technically, fans installed for purposes other than what Air Vent intends them for (and UL for that matter) would not be covered under warranty. As a side note, the motor may likely fail in this application because it could not be air cooled as it would normally. With lots of debris in the air (dust, etc.), it will settle on the motor parts and gum up the works.